Fission-fragment timing with poly-crystalline diamond detectors

For the investigation of prompt and delayed neutron emission in neutron-induced fission the two-arm time-of-flight spectrometer VERDI for high resolution fission-fragment spectrometry is being built at the Institute for Reference Materials and Measurements (IRMM). The ultimate goal is to achieve a mass resolution A/ΔA∼120 in conjunction with a reasonable counting efficiency. One pre-requisite for such a device is the use of ultra-fast timing detectors, which may be operated at high radiation doses. For this purpose poly-crystalline chemical vapour deposited (pcCVD) diamond detectors have been tested for the first time as time pick-up for binary fission fragments. This type of detectors has demonstrated radiation hardness against a mix of alpha-particles, fission-fragments and prompt fission neutrons at radiation doses typically achieved during one fission experiment. For a 1 x 1 cm2 large and 100 μm thick pcCVDD detector an intrinsic timing resolution better than 300 ps has been obtained. Present limitations and possible improvements are discussed.